THE EFFECT OF STOICHIOMETRY ON THE STABILITY AND AC ELECTRICAL-PROPERTIES OF LIXNI1-YCOYO2-DELTA AND LIXNI1-YCOYO2-DELTA-AL2O3 COMPOSITES AT ELEVATED-TEMPERATURES

Polycrystalline samples of LixNi1-yCoyO2-delta(x = 0.6, 0.9 and y = 0. 5, 1, with delta much less than 1 depending on the stoichiometry) with and without the addition of 50 wt% alpha-Al2O3 were prepared and exam ined by XRD, TGA, DTA and a.c. electrical techniques. LixCoO2 and its mixture with alpha-Al2O3 is unstable above 1050 K. Materials containin g Ni were stable up to 1173 K and no interaction with alpha-Al2O3 was found after 6 h at 1173 K. Maximum conductivity in Ar was obtained for Li0.9Ni0.5Co0.5O2-delta between 100 Hz and 1 MHz up to 950 K. The hig h temperature conductivity of Li0.9Ni0.5Co0.5O2-delta could be modifie d with the addition of alpha-Al2O3 to render it suitable for an RF rea ctor. At 650 K the conductivity reversibly increased in CO2 and rapidl y decreased in H-2 followed by a slow increase on removal of H-2, beha viour typical of a p-type semiconductor. At 870 K the conductivity inc reased in H-2 due to slow and irreversible reduction of the oxides.